Catalytic igniter members



Sept. 8, 1970 1'. 1.. COTTON 3,527,680

CATALYTIC IGNITER MEMBERS Filed Dec. 14. 1964 I nvenlor United States Patent U.S. Cl. 204-32 11 Claims ABSTRACT OF THE DISCLOSURE A process for improving the activity of a platinum or platinum alloy catalytic igniter for a gas turbine engine comprises etching the igniter to remove the initial surface layer to increase its activity, plating the member with a layer of platinum which supports catalytic ignition, and heat treating the igniter to improve the hardness and tenacity of the platinum plating.

This invention concerns improvements relating to the production of catalytic igniter members and, although the invention is not so restricted, it is more particularly concerned with a process for improving the activity of a catalytic igniter member employed in reheat combustion equipment of a gas turbine engine.

According to the present invention, there is provided a process for improving the activity of a catalytic igniter member comprising etching the said member to remove the initial surface layer thereof.

If desired, the catalytic igniter member, after having been so etched, is plated or coated with a layer of a material adapted to support catalytic ignition.

We have found that such etching, and, when used, such plating or coating, substantially improves the activity of the catalyst both in the sense that the catalyst is active at lower temperatures than it would otherwise be active and in the sense that it is more active at certain temperatures than would otherwise be the case. Although the reason for this improvement is not fully known, it is thought probable that the reasons may include the removal or covering of a surface film of oxides and the production of more active centres or points of very high activity.

The catalytic igniter member may be made either of platinum or of a platinum alloy. Thus the alloy may for example be a rhodium-platinum alloy containing rhodium.

The catalytic igniter member is preferably constituted by a mesh member.

The etching may be effected by the use of a aqua regia (i.e. a mixture of 25% concentrated nitric acid and 75% concentrated hydrochloric acid) and such etching may be effected by employing warm aqua regia for three minutes. It has been found that any increase in the three minute etching period with aqua regia does not increase the extent to which the activity of the catalyst has been improved.

Since however the use of aqua regia for etching causes the liberation of large quantities of corrosive nitrous fumes during the actual etching process, it is preferred to effect the etching electrolytically, e.g. for at least one hour.

In such electrolytic etching, the catalytic igniter member is made the positive electrode in an electrolytic cell the electrolyte in which is aqueous platinum chloride. Metallic platinum is removed from the surface of the catalytic igniter member when a current is passed through the cell.

When using a catalytic igniter member formed of a 30% rhodium, 70% platinum alloy mesh, it has been found that after electrolytic etching for two hours at a current level of 50 milliamps, the activity at 240 C. was such that 25% of an ignitable mixture was actually ignited, whereas the same catalytic igniter member, when not etched, gave no activity at all until a temperature of 650 C. was reached.

If the catalytic igniter member is electrolytically plated, such plating is preferably effected for not more than three hours, and at a current level not exceeding 30 milliamps. Moreover, the catalytic igniter member is preferably subjected, after it has been plated, to a heat treatment to improve the hardness and tenacity of the plated layer.

Thus, a particularly satisfactory result is obtained by electroplating pure platinum onto the surface of a platihum/rhodium catalytic igniter mesh member. Such a member is first acid etched in order to provide a highly receptive surface for the platinum layer. The member is then made the negative electrode in an electrolytic cell in which the electrolyte is aqueous platinum chloride, e.g. of 30.4 grams/litre strength. The plated layer is of a loose texture after the plating period, but heat treatment for one hour at 600 C. makes the deposit hard and tenacious. This particular catalytic igniter member was also found, as a result of the treatment given to it, to give in creased resistance to contamination by phosphate additives in fuel.

The tenacity of the deposited layer has been found to be inversely proportional to the current density, and hence a relatively low current density should be employed in the plating process.

Yet a further way in which the activity of the catalytic igniter member may be improved is to flash coat a catalyst for five minutes onto the catalytic igniter member.

The invention also comprises a catalytic igniter member when produced by the process set forth above.

The catalytic ignited member of the present invention is especially useful when forming part of reheat combustion equipment of a gas turbine engine.

This use of the catalytic igniter member is illustrated in the accompanying drawing, which is a part-sectional diagrammatic view of a gas turbine engine.

The gas turbine engine shown in the drawing comprises an engine casing 10 within which there are mounted in flow series low and high pressure compressors 11, main combustion equipment 12, an high pressure turbine 13, a low pressure turbine 14, and reheat combustion equipment 15.

The reheat combustion equipment 15 comprises an annular fuel manifold 16 which supplies reheat fuel to a plurality of angularly spaced apart radially extending tubes 17 having apertures 18 through which the fuel may be atomised and may pass into the stream of turbine exhaust gases, which, of course, contain some oxygen.

The turbine exhaust gases carry the atomised fuel to the downstream side of an annular gutter member 20 which provides a sheltered zone for the reheat combustion.

Ignition of the reheat fuel is effected by a catalytic igniter member 21 which is a mesh member through which the fuel-laden turbine exhaust gases pass. The temperature of the said gases, and the nature of the catalytic igniter member 21, are such that the mere passage of the said gases through the catalytic igniter member 21 causes ignition to be effected of the fuel which reacts with the oxgyen contained in the said gases.

I claim:

1. A process for improving the activity of a catalytic igniter member constructed of a metal selected from the group consisting of platinum and platinum base alloys thereof and of the type employed in combustion equipment for igniting a gaseous medium upon contact with said member, said process comprising etching the said member to remove the initial surface layer to increase the activity thereof, plating said member, after having been so etched, with a layer of material adapted to support catalytic ignition, and subjecting said member, after it has been so plated, to a heat treatment to improve the hardness and tenacity of the plated layer.

2. A process as claimed in claim 1 in which the plating is elfected electrolytically for not more than three hours.

3. A process as claimed in claim 2 in which the plating is effected at a current level not exceeding 30 milliamps.

4. A process as claimed in claim 1 in which said cat-- alytic igniter member is a mesh member.

5. A process as claimed in claim 1 in which the etching is effected by use of aqua regia.

6. A process as claimed in claim 1 in which the etching is effected electrolytically.

7. A process as claimed in claim 6 in which the etching is eifected for at least one hour.

8. A process as claimed in claim 1 in which said member is formed of platinum.

9. A process as claimed in claim 1 in which said member is formed of a rhodium-platinum alloy containing 20%-30% rhodium.

10. A process as claimed in claim 1 in which the plated material is platinum and in which the plating is effected electrolytically.

11. In the process of catalytically igniting a gaseous medium by contacting it with a catalytic igniter member constructed of a metal selected from the group consisting of platinum and platinum base alloys thereof, the improvement which renders said catalytic igniter active at lower temperatures and more active at certain temperatures, said improvement comprising etching said catalytic member to remove the initial surface layer to increase the activity of said member, plating said etching member with a layer of a metal which supports catalytic ignition, and then hardening and improving the tenacity of the layer by heat treating said plated member.

References Cited UNITED STATES PATENTS 821,042 5/1906 Kitsee 204146 XR 2,344,208 3/1944 Kirkpatrick 252 23s 2,470,033 5/1949 Hensel 2 04-47 XR 2,720,494 10/1955 Suter et al. 204442 XR 2,996,944 10/1961 Chessin et a1. 204 42 XR 3,116,165 12/1963 Hipp 117'-217 JOHN H. MACK, Primary Examiner W. B. VANSISE, Assistant Examiner US. Cl. X.R. 11750; 20437 

